3 Answers
3

To use these spells, you cast the spell and then touch the subject. In the same round that you cast the spell, you may also touch (or attempt to touch) as a free action. [...] You can automatically touch one friend or use the spell on yourself, but to touch an opponent, you must succeed on an attack roll.

A handshake is a form of a touch, so go for it. The main question is whether or not a "charge" from a touch spell or the effect of discharging such a spell is visible.

Maybe in the case of ranged spells used as a Ranged Touch Attack.

Compare the description of Chill Touch:

A touch from your hand, which glows with blue energy, disrupts the life force of living creatures.

To Ray of Enfeeblement:

A coruscating ray springs from your hand.

Ranged Touch Attacks by and large work like Ray of Enfeeblement: A laser-beam or other thing not affected by armor attacks your target.

The DM could rule that a beam that originates from your hand is guaranteed to strike someone you're shaking hands with... But they could just as easily argue that the beam originates from the tip of your index finger and goes flying off into nowhere, or that the target's hand isn't a direct enough hit for the spell to take effect.

Other Ranged Touch Attack spells may have different descriptions, making them easier or harder to perform against someone you're shaking hands with.

The issue here is one of language. Ranged Touch Attacks are not "touch" from a description standpoint ("attacks like touching someone, but from an arbitrary distance"), they are "touch" from a mechanical one ("attacks that bypass armor in the same way as the touch attack mechanic").

One last note: If the person shaking your hand perceives you spellcasting (say, because you don't have the feats to hide Verbal and Somatic components), I would rule that they could drop the handshake as a reaction to your spell casting unless you had something special stopping them (Bigby's Crushing Handshake?).

Tangential question to the points you make: If two diplomats are shaking hands to negotiate a peace and my character wants/needs the war to continue, can he use a ranged touch attack spell (assuming there's an invisible "laser beam") and target when the two shake hands? Would that target both in the handshake, or the diplomat of my choice?
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PulseheadJun 17 '12 at 2:18

@Pulsehead A "Ranged Touch Attack" doesn't really have anything to do with "touching" from a flavor standpoint. It just happens to use the same AC numbers as a touch attack. So like any ranged attack, you'd choose a single target (unless directed otherwise by the spell).
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AceCalhoonJun 17 '12 at 5:34

You have to understand the difference between Ranged Touch Attacks and Touch Attacks. A Touch Attack is an attack that bypasses physical armor. This is used for times when actually penetrating the armor is immaterial. A Ranged Touch Attack is an attack that bypasses armor, but is taken at range. It does not require the player to actually touch the target. Instead, it requires the attack effect to touch the target. This is used to represent splash damage and ranged spell damage.

The description of Ray of Enfeeblement says "a coruscating ray springs from your hand" (emphasis mine). Coruscating means "flashing, sparkling, brilliant". It also has a range of 25' + 2'/level. This means that a sparkling ray shoots from your hands, but merely needs to touch the target without penetrating their armor. Unless the subject is blind, I'd say they're going to see that ray coming and would have the same opportunity to dodge as everyone else in a combat1. They may be Flat-Footed and thus lose their Dex, but they still have an AC.

The description of Chill Touch states "a touch from your hand, which glows blue with energy". Again, I'd say that the target would, unless blind, notice and get his AC.

If you can come up with a situation where the target is truly unaware the attack is happening, I would rule that target helpless and use the Coup de Grace rules. Otherwise I would make my players roll to hit. Tanstaafl.

1 Actually, if this situation came up in a game I was running, I would likely rule that these spells had some similar audio and olfactory manifestations as well. Blind, therefore, would not be enough. However this is DM fiat and not RAW.

I would say if you cast a non-flashy touch spell, held the charge and then within the minute walked up and shook someones hand you would not need to roll to hit. But expect appropriate NPC reactions from those arround you.

A ranged touch spell or flashy touch spell (like Chill Touch which has a very visible effect) would not work the same.